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Topic:
Ground Loop on HDMI to Sub help
This thread has 28 replies. Displaying posts 16 through 29.
Post 16 made on Sunday July 29, 2018 at 09:56
highfigh
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On July 29, 2018 at 00:06, Ernie Gilman said...
a couple of changes for clarity....
wait wait wait wait wait wait...
What voltage test light? 12 volts for car use? Neon? Plain old 120V light bulb in a socket? It's possible to have current flowing through a ground and creating hum, but with too little current to light any actual bulb. More details are needed to this right.

Really? A neon test light? Are we dealing with such high voltage on cable feeds?

I'm not the first to recommend using a test light for this and it has been discussed before.

I measured 15V on the cable coming to my cable box after reaching in with one hand to break the connection while my arm was laying on the cover. Nice tingle, but at least it wasn't passing through me. I had been seeing noise bars, so I disconnected it to verify my thinking- it did. I didn't bother with a test light at the time because I had already found that voltage was present but one made for 12V will work because it will be dim with low voltage and that's enough to cause a problem.

If it hums, it will light a bulb that's used for low voltage.

Some LEDs can be used for this, but I haven't checked the voltage when my capacitor discharger fades out.
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
Post 17 made on Sunday July 29, 2018 at 21:34
Ernie Gilman
Yes, That Ernie!
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I'm just really saying that if you are trying to give technical help and you suggest using a test device, the device should be defined. Otherwise it's just a light thingie.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 18 made on Monday July 30, 2018 at 00:07
Ernie Gilman
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I just ran across Rane 110, located at [Link: rane.com]. It's a white paper that explains grounding problems in audio interconnections. You'll probably understand all of it, but if you don't, you'll pick up some information from it.

Enjoy.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 19 made on Monday July 30, 2018 at 09:06
highfigh
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On July 30, 2018 at 00:07, Ernie Gilman said...
I just ran across Rane 110, located at [Link: rane.com]. It's a white paper that explains grounding problems in audio interconnections. You'll probably understand all of it, but if you don't, you'll pick up some information from it.

Enjoy.

You finally ran across that? That, along with the Jensen Transformers white pages, have been posted here many times in threads about ground loops. I bookmarked their white pages link around ten years ago and initially attended a Jensen Transformers talk on grounding in 1980. While it was specifically for 12V audio, the principles are the same. Went to another for AV at CEDIA in 2005- Bill Whitlock spoke at both. If you get a chance, go- it's definitely worthwhile. If you can't, YouTube has a lot of videos-

[Link: youtube.com]
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
Post 20 made on Monday July 30, 2018 at 13:04
Ernie Gilman
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Yes. All true.

Don't forget that not all the people using our help are as antique and hep to the jive as you and I. I finally ran across it? No. I ran across it again. It tells me nothing new. Really. But this site is not just "Dinosaur Chat" -- It's also a place where new people can run across information that's new to them.

They can't bookmark it if they haven't heard of it. Don't put down the offer of information to people other than yourself.

For that matter, why bookmark it? Why not download the white papers? That way you won't have to have internet to look at them.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 21 made on Tuesday July 31, 2018 at 09:29
andrewinboulder
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On July 27, 2018 at 18:10, kwkshift said...
If you can't find the source of the hum, either one of these should solve your problem:

[Link: amazon.com]

[Link: amazon.com]

I have used both in the past with perfect results.

I've used that Rolls piece and it worked perfectly. I keep one on the van now. Never seen that outlet thinga-ma-jig though. Interesting.
Post 22 made on Tuesday July 31, 2018 at 12:56
Ernie Gilman
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Watch the videos on the Ebtech product, since the vendor clearly explains the conditions under which that device won't help. There's no point in just buying one to try if the manufacturer has told you when it won't work! Not at eighty bucks, that is.

Edit: Unfortunately, the Hum X plugs directly into 120V Power, but the literature on it on their site does not mention "UL" at all. That suddenly gives me pause.

Last edited by Ernie Gilman on July 31, 2018 13:22.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 23 made on Tuesday July 31, 2018 at 18:08
Mr. Brad
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It would be nice if we heard back on the success of resolving the problem.
Post 24 made on Wednesday August 1, 2018 at 09:16
lippavisual
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Hum X works a treat. I've been using them for years and have installed them in clients homes without hiccups.

I used to just go grab them at Guitar Center that was close to me.
OP | Post 25 made on Wednesday August 1, 2018 at 09:59
SWOInstaller
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On July 31, 2018 at 18:08, Mr. Brad said...
It would be nice if we heard back on the success of resolving the problem.

Yes Brad, Sorry I have been busy. I will try to answer all outstanding questions that are relevant to the situation, as well as my findings.

On July 28, 2018 at 03:22, davidcasemore said...
How is the sub connected to the Denon? Seventy Feet of unbalanced audio? I see from the specs that this sub does not have a balanced (XLR) input and the Denon doesn't have a balanced output so you either did 70 ft. of unbalanced (Hum, Hum, Hum, Hum, Hum) or you used the speaker terminals (really? People do that?)

No balanced audio, yes 70' of unbalanced RCA terminals on each end of coax connected directly into amp and sub

On July 28, 2018 at 04:39, King of typos said...
I don’t know if I missed reading it, or no one suggested it...

How about swapping the cable box with one of the other boxes? If the problem goes away, well that box is bad. This can go with the power block, that is if the power supply isn’t built into the box.

Tried that, hum was still present

Also, since the sub and av are on different circuits. Is it possible they are on different panels too? If so, that could be a problem in itself. They could be on the same phase, but different panels. Thus the sub panel can not have the grounded (neutral) and grounding (ground) bonded together like they can in the main panel.

Different circuits, same panel (only one in the house), not sure about what phase each circuit is on.

On July 28, 2018 at 08:20, highfigh said...
Did you disconnect the coax at the demarc box? If you do that and the hum stops, call the cable company and have them fix their system.

Yes hum stops when demarc cable disconnected from system. Tried grounding internal house demarc (cable company didn't) but did not resolve the issue. Informed customer to contact cable company to resolve.
You can't fix stupid
Post 26 made on Wednesday August 1, 2018 at 12:51
Ernie Gilman
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Let's pin down the terms. The demarc is the place of separation between the cable company's wire and your house's wiring. It's a "grounding block," which is an F81 built so there's a place to insert a wire, up to 12 ga or so, that is run to an electrical ground. The standard setup has the cable company wire coming in on the left, the house wiring going out on the right, and the ground wire, a green wire, going to a ground, which ideally is at the power inlet to the house. It can also be a ground rod, sometimes even a water pipe. It should not be the ground of an outlet, but sometimes that's done and it can work.

When you write, presumably "demarc cable" means the cable from the cable company and "internal house demarc" is the cable going from the grounding block to all the house cable wiring. Right? That is, there's a ground block somewhere with the "demarc cable" coming from the cable company and the "internal house demarc" going to the house wiring, and the hum stops when undo the house wiring from that grounding block.

Why all this tedious statement of what we already know? Because I've never seen the term "demarc cable" and "internal house demarc," and while it should be clear just what that means... well, read my signature and think about times when perfectly obvious things have been misunderstood.

What are the details of how you tried grounding the grounding block? Connect to the chassis of the power boxes. If those are nowhere near the demarc, a water pipe might work. If not, the cable company might have to move the cable drop to where they can connect to a good ground. That might not be possible.

But if you temporarily add a ground by running a wire from the demarc to the power boxes and the hum goes away, you will prove to the cable guy that the problem is HIS GROUND and he needs to fix it, no matter what it takes.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 27 made on Wednesday August 1, 2018 at 13:48
buzz
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Disconnect the cable feed at the entrance of the house, then measure the voltage between the shields from the street feed and and the house. Take care while doing this because there could be an unexpectedly high voltage here. I've seen installations where the voltage is so high that there is a visible spark as the connection is made or broken. If this voltage is significant, you'll need to be anal about your grounds.

You should also measure the voltage between the electrical system ground and the cable system shield. This voltage should be near zero. There should be a wire "bond" between the electrical system ground and the cable grounding block. Simply having a separate ground rod for both is not good enough, the rods must be bonded. Why should they be bonded? Even if there is no voltage difference between the shields, there can be very large voltage differences between ground rods immediately after a nearby lightning strike. If a human or piece of equipment is trapped between warring ground rod potentials, there can be serious consequences.
Post 28 made on Thursday August 2, 2018 at 09:28
highfigh
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On August 1, 2018 at 12:51, Ernie Gilman said...
Let's pin down the terms. The demarc is the place of separation between the cable company's wire and your house's wiring. It's a "grounding block," which is an F81 built so there's a place to insert a wire, up to 12 ga or so, that is run to an electrical ground. The standard setup has the cable company wire coming in on the left, the house wiring going out on the right, and the ground wire, a green wire, going to a ground, which ideally is at the power inlet to the house. It can also be a ground rod, sometimes even a water pipe. It should not be the ground of an outlet, but sometimes that's done and it can work.

When you write, presumably "demarc cable" means the cable from the cable company and "internal house demarc" is the cable going from the grounding block to all the house cable wiring. Right? That is, there's a ground block somewhere with the "demarc cable" coming from the cable company and the "internal house demarc" going to the house wiring, and the hum stops when undo the house wiring from that grounding block.

Why all this tedious statement of what we already know? Because I've never seen the term "demarc cable" and "internal house demarc," and while it should be clear just what that means... well, read my signature and think about times when perfectly obvious things have been misunderstood.

What are the details of how you tried grounding the grounding block? Connect to the chassis of the power boxes. If those are nowhere near the demarc, a water pipe might work. If not, the cable company might have to move the cable drop to where they can connect to a good ground. That might not be possible.

But if you temporarily add a ground by running a wire from the demarc to the power boxes and the hum goes away, you will prove to the cable guy that the problem is HIS GROUND and he needs to fix it, no matter what it takes.

It's possible that the voltage is on the center conductor, too. We should all be carrying DC block connectors in our vehicles or RF kits. This would probably help, but I would start with grounding the feed's shield. If that doesn't cure it, install the block and see if that does.

Once the source of the hum is discovered, the cable company should be informed, so they can fix THEIR system. The need for a DC block usually indicates a bad amplifier.
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
Post 29 made on Thursday August 2, 2018 at 10:06
Ernie Gilman
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It's possible for there to be DC on the center conductor, but that won't cause hum. DC is zero Hertz -- just a constant voltage. Hum is 60 Hz or 50 Hz.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
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